(Photo by Joe Raedle/Getty Images)

As measles spreads across parts of the U.S. like some 21st-century plague, many concerned persons have begun to wonder how anti-vaccination beliefs still persist, exactly.

Maybe it’s the manifestation of a deeper culture war, some suggest. Maybe it’s rooted in psychology. Or class inequality. Or good old-fashioned stubbornness.

Now there’s evidence that this particular strain of nonsense incubates in the same petri dish as most other Internet inanities. According to a forthcoming paper from researchers at Washington State, consumers making decisions about vaccines are heavily influenced by … online comments. They’ll even trust the medical opinions of the anonymous Internet hordes over, say, the government agency charged with monitoring such things.

“We observed, much to our surprise, that participants were equally influenced … [by] online commenters as they were by the public service announcements from the Centers for Disease Control and Prevention,” explained Ioannis Kareklas, the lead author on the paper. In other words, regardless of whether they’re pro- or anti-vaxing, people take strangers’ opinions on vaccination very seriously.

To come to this conclusion, Kareklas and his colleagues basically set up two separate experiments. Experiment 1: Show people a PSA on vaccination, either pro or con, along with some anonymous comments, and see how that changes their feelings towards vaccinating themselves and their families. Experiment 2: Show people a PSA again, but now give the commenters identities — a doctor who studies infectious disease, for instance, or an undergraduate English student who presumably knows nothing about vaccinology.

The second experiment was heartening: People took the opinions of the doctor much more seriously than those of the student. But when the professions of the commenters were not explicitly revealed — in other words, when the experiment mimicked the actual conditions of every comments section on the Internet — readers were just as influenced by the content of the PSA as they were by the comments.

This isn’t just about PSAs, either, Kareklas told me. He believes their findings about comment-section influence apply to any online setting: say, a sober news story about the science of vaccination. So while my colleagues Lenny Bernstein and Charity Brown put together this excellent, no-nonsense, meticulously researched guide to measles, all their educative efforts could be undone by … the first three anonymous comments.


This research, incidentally, backs up some of the questions media organizations have raised about the comments section before; when PopSci.com famously deleted its comment section in September 2013, the site’s content director explained that she worried about the impact that comments had on science: “commenters shape public opinion; public opinion shapes public policy; public policy shapes how and whether and what research gets funded–you start to see why we feel compelled to hit the ‘off’ switch.” Despite the fact that Popular Science is a century-old magazine with a long track record of excellent reporting on technology and science, its editors feared that readers were as influenced by trolls in the comment section as they were by the reporting in the magazine itself.

The kicker? They were right, basically! (Karaklas said his team’s study was actually inspired in part by Popular Science’s decision to shut comments down.)

That said, researchers don’t think that’s necessarily the right move — even where critical public health issues are concerned. Instead, if concerned organizations want to combat misinformation about vaccines (or anything else), they should make sure to get some experts in the comments section, too, and clearly mark them as such.

“We don’t think that the CDC should take down comments from individuals who argue against vaccines,” Karaklas said, “we think they should ensure that pro-vaccine comments from vaccinology experts are easy to find and plentiful on their website.”

Alas, they may be difficult to do. Vaccinology experts, here’s some Post coverage on the subject — now it’s your move!